Apparatus for and method of sampling intermediate products of chemical reactions



Jan. 29, 1963 L. H. s. RoBLEE, JR., ETAL 3,075,391

APPARATUS FOR AND METHOD OF SAMFLING INTERMEDIATE PRODUCTS OF CHEMICAL REACTIONS v 4 Sheets-Sheet, l

Lelond H. S. Roblee, Jr. Inventors Stevens C. Sperling Potent Attorney Jan. 29, 1963 Filed Dec. 30. 1960 APPARATUS FOR ND METHOD OF SAMP'LING INTERMEDIATE L H s. RoBLEE, JR. ETAL 3,075,391

PRODUCTS OF CHEMICAL REACTIONS 4 Sheets-Sheet. 2

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Lelond H. S. Reblee, Jr. Inventors Stevens C. Sperling By Po ent Attorney Jan. 29, 1963 APPARATUS FOR AND METHOD OF SAMPLING INTERMEDIATE Filed Dec. 30. 1960 L. H. S. ROBLEE JR. ETAL PRODUCTS OF CHEMICAL REACTIONS Leland H. S. Roblee, Jr. Stevens C. Sperling 4 Sheets-Sheet 3 Inventors- Patent Attorney Jan- 29, 1963 H. s. ROBLEE, JR., ETAL 3,075,391

APPARATUS FOR AND METHOD OE sAMPIINC INTERMEDIATE PRODUCTS OE CHEMICAL REACTIONS Filed Dec. 30, 1960 4 Sheets-Sheet 4 @Qt o @mmo d H 3 Ewa @we n III zommzoo o @zu o wn. me f1l ws @952mg v550 NGE 32082.22 z MEF Q m w m m N o u L d. nu smh. x S nu w: cozmno 55o zowmoo o DE 3 Banssaad Leland H. S. Roblee, Jr. Inventors S'revens C. Sperling By m Pa ent Attorney arrasar' Patented Jan.` 29, l 953 ice 3,075,391 APPARATUS FR AND METHOD OF SAMPLING ENTERMEDATE PRDUCTS GF CHEMICAL RE- ACTIGNS Leiand H. S. Rabies, Jr., and Stevens C. Sperling, Metuchen, NJ., assignors to Esso Research and Engineering Company, a corporation of Delaware Filed Dec. 30, 196i), Ser. No. 79,7?3 7 Claims. (Cl. i3-421.5)

This invention relates to an apparatus for and method of obtaining samples of intermediate products of chemical reactions, that is, products of reactions which have not gone to completion. It relates particularly to an apparatus for and method of obtaining samples of intermediate products of precombustion reactions of fuel/ air mixtures, such reactions taking place at both high pressures and high temperatures as within the cylinders of an internal combustion engine.

The effects of various chemical and physical parameters on knock phenomena in spark-ignited engines have been studied extensively. Important among the studies made have been those in which (a) pressure and temperature variations during the engine cycle were measured; (b) chemical analyses were made of partial and complete combustion reaction products, and (c) cool llames were detected in motored engines. In all these studies, however, the continuously changing engine conditions have greatly complicated interpretation of the measurements obtained. To provide a more controllable and constant environment for the study or precombustion reactions, a number of special machines for compressing gases called rapid compression machines have been designed and built.

With such a machine, a combustible mixture can be compressed very rapidly and very nearly adiabatically to a preselected pressure and temperature, and maintained at constant volume until autoor spontaneous ignition occurs. This compression is accomplished by motion of a piston in a closed-end cylinder. The piston-cylinder combination may have a variable compression ratio. Through the use of high speed strip -lm cameras and a rapid-response pressure transducer, traces representing piston motion during compression and combustion charnber pressure during and after compression are obtained. From these traces the ignition delay time, defined as the time from the end of compression to autoignition (peak pressure) may be determined.

Previously, studies based upon records taken from rapid r or adiabatic compression machines have been concerned primarily with the physical aspects of autoignition, and have increased the state of knowledge of combustion phenomena considerably. A great deal remains to be determined, however, about the mechanism of precombustion reactions. Although research into the chemistry of these reactions at low pressures and fairly high temperatures have been extensive, only a limited number of studies have been made at conditions of both high pressure and high temperature.

According to the present invention, a device has been constructed for attachment to a rapid or adiabatic cornpression machine by means of which itis possible to follow the chemical-time histories of high pressure and high temperature precombustion reactions. This device comprises an expansion chamber connected to the combustion chamber of the adiabatic compression machine, the form of the expansion chamber being that of a long, slim tube extending from the combustion chamber which terminates in a relatively enlarged and speciallyshaped region. It comprises further a rupturable diaphragm whereby the expansion chamber is normally separated from the combustion chamber. It comprises still further a catch-retained, spring-loaded probe whereby the separating dia phragm may be ruptured, and it comprises even still further a solenoid whereby the retaining catch of the probe may be withdrawn, this solenoid being energized at a selected instant in synchronism with the action of the adiabatic compression machine by means of a variabletime relay.

In its operation, the apparatus of this invention functions to expand rapidly and thereby cool or quench the fast, gas-phase reactions which occur during ignition delay. This expansion-type cooling or quenching action is achieved by shock technique upon rupturing of the diaphragm. At the moment oi diaphragm rupture, the difference in pressure between the combustion chamber and the expansion chamber causes a ilow of high pressure, partly reacted gaseous materials from the combustion chamber into the yrelatively low pressure gas (helium, for example) in the expansion chamber. Within a few diameters of the tubular portion of the expansion chamber, a pressure lshock wave develops which propagates through the expansion chamber at a velocity greater than that of sound relative to the gases at rest in this chamber. Simultaneously, and in the opposite direction, a rarefaction wave propagates into the combustion chamber. This wave reduces the high pressure and high temperature of the partially reacted gases developed on compression and during the ignition delay to much lower values.

The shock wave meanwhile will have passed along the full length of the tubular portion of the expansion charnber. If this chamber were of uniform cross section for its full length and terminated in a simple transverse plate which could be struck by the shock wave, this wave upon so striking would be reflected as a pressure wave heading back along the expansion chamber toward the combustion chamber. Upon reaching this chamber or at least the front of the rarefaction wave, and impinging upon the incompletely reacted but quenched gaseous materials within the combustion chamber or at least within the expansion chamber beyond the rarefaction wave front, the reected shock wave would induce additional precombustion reaction in the previously quenched mixture.

To prevent the induction of such additional precombustiou reaction, the expansion chamber is provided with the aforementioned enlarged region at its end more distant from the combustion chamber. There is an abrupt increase in cross section area of the expansion chamber at the juncture of its long, slim tubular portion and its er1- larged region, the latter being of comparatively short length. lt is within this enlarged region that the front of the pressure shock w-ave can expand, and this wave dissipate its force without significant reflection back out of this region. Such dissipation is aided by special shaping of the wall of the enlarged region of the expansion chamber most distant from the combustion chamber. For shock wave dissipation purposes, it is advantageous that this wall be convex toward the tubular portion of the expansion chamber, and hence convex toward the cembuston chamber of the adiabatic compression machine.

Ultimately, and relatively rapidly after rupturing of the diaphragm initially separating the combustion chamber of the adiabatic compression machine and the eX- pansion chamber of the apparatus of this invention pressure surges within the whole space dened by the combustion and expansion chambers will die out. The entire mass of gaseous materials therewithin will come to a condition of both low pressure and lo-w temperature, and will represent a mixture of quenched precombustion reaction products and the material charged into the expansion chamber prior `to diaphragm rupture. This mixture may be transferred by a suitable conduit arrange- 3 ment from the combustion and expansion chamber space to a container vessel or coil immersed in liquid nitrogen (-l96 C.) for storage prior to analysis. The material so transferred will represent a sample of precombustion reaction products as these products existed at a determinate point in time during the delay period of the compressed fuel/air mixture in lthe cylinder of the adiabatic compression machine.

The nature and substances of this invention will be more clearly perceived and fully understood by referring to the following description and claims taken in connection with the accompanying drawings in which:

FIG. 1 represents a partly structural, partly schematic arrangement of the sampling apparatus of this invention and associated electrical and piping systems connected to an adiabatic compression machine;

FIG. 2 represents a View in longitudinal section of the expansion chamber and diaphragm puncturing device of the apparatus of this invention connected to the head end of an adiabatic compression machine;

FIG. 3 represents an enlarged view in longitudinal section of the head end `of the adiabatic compression machine of FIG. 2, particularly illustrating lthe diaphragm whereby the combustion chamber of the adiabatic compression machine and the expansion chamber yof the appar-atus of this invention are separated;

FIG. 4 represents a perspective view taken in section along line 4 4 in FIG. 3 showing details of the support and guidance means of the diaphragm puncturing probe of the apparatus of this invention near the end of this probe adjacent the diaphragm;

FIG. 5 represents a pressure-time trace showing the additional precombustion reaction caused by a retiected shock wave in a stoichiometric mixture of benzene and air within the combustion chamber of an adiabatic compression machine, this mixture having been previously quenched by shock cooling at a point part way through its ignition delay period following the compression stroke 'of the machine;

FIG. 6 represents a pressure-time trace showing the quench according to the method of this invention of a stoichiometric mixture of benzene and air within the combustion chamber of au adiabatic compression machine at a point three quarters through the ignition delay period of the mixture following the compression stroke of the machine, and

FIG. 7 represents a pressure-time trace showing the quench according to the method of this invention of a stoichiometric mixture of benzene and air within the combustion chamber of an adiabatic compression machine at the end of the compression stroke of this machine.

Reerring now to the drawings in detail, especially to FIG. 1 thereof, a rapid or adiabatic compression machine is generally designated 10. This machine has a pneumatically-actuated compressing mechanism assembly 12 and a combusti-on chamber assembly 14. It is by means of compressing mechanism assembly 12 that a piston closing one end of 'the combustion chamber of machine 10 is driven rapidly t-o the right to effect an essentially adiabatic compression of gaseous material such as a fuel/ air mixture charged into the combustion chamber. It is to be understood that mechanism assembly 12 does not operate continuously through a series of cycles. Instead it is released from what may be considered a cocked condition to move the machine piston in a single compressing stroke and hold it firmly at the end of this stroke.

In one design of an adiabatic compression machine with which experiments using the apparatus and method of the present invention have been performed, the actuating agent is compressed nitrogen gas. The piston mechanism against which this compressed gas operates is retained initially in a starting or retracted position by means of a shear pin, and this pin is sever-able by means of a plunger designated 16. For triggering of adiabatic compression machine 10, plunger 16 is struck by the weighted end of pendulum 18 pivoted on a base structure 19 having a xed location with respect to the adiabatic compression machine. The pendulum, which is shown in solid and dashed outline in its raised and lowered positions respectively, is held normally in its raised position by solenoid-operated latch mechanism 20. This mechanism may be energized by closing switch 22 to become disengaged from pendulum 18, and allow the pendulum to drop.

Combustion chamber -assembly 14 of adiabatic compression machine 10 is charged from tank 24 containing a fuel/ air mixture such Ias a mixture of benzene and air. Connection is made from tank 24 to `the combustionr chamber assembly through conduit 26, valve 28, conduit- 30, conduit 3-2, and valve 34. Gaseous waste or exhaust. material is removed from the combustion chamber asf sembly through conduit 36, valve 38, and vacuum pump 40. Indication of fuel/air mixture supply pressure and of the pressure of certain other charging and/or liushing gaseous materials to be mentioned presently is provided by manometer 42 connected to conduit 30.

A pressure-to-voltage transducer or pressure pickup 44 is set in the head end of combustion chamber assembly 14. This pickup is connected electrically by transmission means 46 to the signal input side of electronic amplier 48 which may be of any suitable design. This amplifier is connected in turn from its output side by transmission means 50 to the signal input side of an oscilloscope 52 which may be likewise of any suitable design. Aligned with the viewing face of the oscilloscope is a high speed strip lm camera 54. Operation of this camera is controlled by switch 56 which is connected electrically to it by transmission means 58.

Switch 56 is so located that when it is in the open or off position its lever, button, or other actuating element subject to external manipulation may be struck andi passed by falling pendulum 18. Upon being so struck, the lever, button, etc., of switch 56 throws the switch into the closed or on position, and the switch stays in such position even though pendulum 18 has passed it until it is intentionally reopened or turned to oli Once switch 56 has been closed, camera 54 is started and proceeds to make a photographic record of the pattern appearing on the face of oscilloscope 52. The record so taken will be a pressure-time trace of events within the cylinder of adiabatic compression machine 10.

A sampling device generally designated `60 constructed according to the present invention is set in the head end of combustion chamber assembly 14. This device com prises an expansion chamber including a relatively long, slim tubular portion 62 extending outwardly from adiabatic compression machine 10 and a relatively short, abruptly transversely enlarged and specially shaped region or portion 64 at the end of tubular portion 62 distant from the combustion chamber. The feature of special shaping of expansion chamber enlarged portion 64 lies in the contour of its interior w-all surface farthest removed from the adiabatic compression machine. This surface shown in dashed outline and designated 66 is convex toward expansion chamber tubular portion 62, and so convex toward the head end of adiabatic compression machine 10.

The expansion chamber portions of sampling device 661 are normally separated from the combustion chamber of' the adiabatic compression machine by a thin diaphragm.. This diaphragm (not shown in FIG. 1, but illustrated in. FIGS. 2 and 3) is located at the end of expansion cham-- ber tubular portion `62 adjoined to combustion chamber assembly 14. Within the sampling device and forming part of it is a diaphragm puncturing probe y68 which is supported essentially axially within expansion chamber portions 62 and 64 and guided therewithin in longitudinal motion. Probe 68 is spring-loaded toward the lett, and

terminates at its right hand end yin a cocking knob 70. The probe is retained in its right hand or cocked position by the plunger element of electrical solenoid i2 which -is itself part of sampling device do.

Prior to rupture of the diaphragm, the expansion charnber space within sampling device di? is customarily charged with an inert gas such las helium to a positive pressure, a pressure of about p.s.i.g. for example. This inert gas is admitted to the sampling device through conduit 74, valve '76, conduit Sil, conduit 78, and valve 8o. At the end of a sampling run, a mixture of this gas and the Iprecombustion reaction products are Withdrawn from the combustion and erpansion chamber spaces through valve 80, conduit 7d, conduit 3i?, conduit d2, valve 34, collecting vessel 86, valve ifand conduit 9o. This withdrawal is elected by Vacuum vpump 92.

Collecting vessel $6, which may be in the form of -a coil, is immersed in a body of liquid nitrogen 9e contained in a Dewar or thermos flask 96. Helium and other very low boiling materials withdrawn from the combustion and expansion chamber spaces will be discharged completely from the system at the outlet of vacuum pump 92, but the greater part of the withdrawn materials and particularly the greater part of the precornbustion reaction products will be condensed and retained in collecting vessel 36. A suitably decreased pressure reading at manometer 42 tells when the system has been pumped down, and the rate of decrease of this reading is a guide to pumping speed. After an adequate and representative sample of precombustion reaction products has been collected in vessel 86 as indicated by a low reading at the manometer, Vvalves 88 and 84 are closed and operation of vacuum pump 92 is discontinued. Container vessel Sie may then be disconnected from the system at iianges or otherconduit couplings beyond valves @d and SS. The sample material retained in vessel or coil Se may be stored for an indefinite length of time prior to analysis, ln the meanwhile, of course, the apparatus of FlG. l may be used with other container vessels for the gathering of additional samples of precombustion reaction products.

`When sampling device do is installed on adiabatic compression machine 10 with a fresh, unruptured separating diaphragm, there may still be traces of reaction products left within expansion chamber portions 62 and 64 from a previous sampling run. The expansion chamber space should be iiushed of any such traces before another sampling run is undertaken. Such liushing may be eiiected by helium admitted through conduit 7d, etc., al-

lowed to mix with and dilute the trace gases, and then withdrawn by vacuum pump 92. As a measure to conserve helium, initial ilushing may be effected by air admitted to sampling device 66 through conduit 98, valve itin, conduit Bil, conduit 7S, and valve Sil. in these llushing operations as well as in theoperation of vacuum pump 92 to remove precornbustion reaction products from the sampling device for storage in collecting vessel do, it will be desirable to isolate the right hand side of conduit 3d to which sampling device 6d is connected from the left hand side of this conduit to which adiabatic compression machine lo is connected Such isolation can be effected by closing valve E102.

As noted hereinbefore, diaphragm puncturing probe 6d of sampling device 6d is held to the right in its cocked position by means of the plunger element of solenoid 72. This solenoid is connected electrically by transmission means lod to the output terminal or terminals on the external or power side oi quick acting, variable-time relay lli-Ii. Operation of this relay is controlled by switch .ldd which is connected electrically to its coil side by transmission means llltl. Switch los is so located that when it is in the open or olf position its lever, button, or other actuating element subject to external manipulation may be struck and passed by falling pendulum 13. Upon vbeing so struck, the lever, button, etc., of switch dit@ '6 throws the switch into the closed-or on position, and the switch stays in such position even though pendulum i3 has passed it.

Closing of switch M8 energizes the delay circuit in relay lilo. This circuit may be of any Well known design having the characteristic of being adjustable to give a relatively broad range of response times. At the end of the preselected response or delay time when sulicient current has built up in its actuating system, relay 166 is closed on its external or power terminals. When the relay is so closed, power is supplied to the coil element of solenoid 7'2 to raise the solenoid plunger element and release the diaphragm puncturing probe. This probe will then be driven to the left by its loading spring, and Will effect initial rupture of the diaphragm separating the combustion and expansion chamber spaces. After this initial rupture, the whole diaphragm will be collapsed very vswiftly by the highly compressed gases acting against it from the combustion chamber side, there being relatively very little supporting pressure exerted upon the diaphragm .from the expansion chamber side.

Considering the whole sampling and recording system shown in FIG. 1, it should be observed particularly that three significant and synchronized sequences of events are started by the closing of switch Z2 to energize solenoidtype latch Ztl and release pendulum ILS. These sequences are (1A) closing of switch 16S and energizing of solenoid '72 to release diaphragm puncturing probe 63, (2) closing of .switch 56 and starting of camera 54, and (3) striking of plunger 16, shearing of the pin whereby the piston mechanism of adiabatic compression machine lll is held in cocked position, and very rapid motion of this machines vpiston to the right to compress the charge of fuel/air mixture within its cylinder.

Initiation of the leftward motion of probe d' may be regulated with respect to the action of the adiabatic compression machine by the variable-time feature of relay lilo. The time delay available in this relay will be added to that characteristic of solenoid 72, and this sum added to the time required'for the loading spring of probe 68 to drive this probe from its cocked position following release to a position wheerin it punctures the separating diaphragm to give the total time needed or available from closing of switch 108 to diaphragm rupture. Variation of this time through adjustment of relay lilo will give a relatively earlier or later moment of rupture, and consequently an earlier or later initiation of the shock phenomena described hereinbefore. This in turn hastens or retards the quenching of the precombustion reaction going on within the cylinder of the adiabatic compression machine.

Referring next to FIGS. 2, 3, and 4, the structure of combustion chamber assembly lid includes a cylinder 112. Shouldered within this cylinder is a spacing ring H3, and abutting this ring is a cylinder head 114 into which pressure pickup 44 is tted eccentrically. Spacing ring 113 may be made in a range of axial thicknesses to allow variation of the head end clearance and thus variation of the compression ratio of the adiabatic compression machine. Cylinder head llllfl is borne upon by a collar llo which is borne upon in turn by a clamping ring lll. Ring 11S is pulled down tightly on collar llo by means of a plurality of bolts IlZll which pass through clear holes in the ring, and thread into tapped holes in the head end of cylinder M2. T he heads of these bolts are offset from the surface of ring M8 by means of washers T ZZ. Cylinder head 114 is bored axially all the way through, and additionally iS counterbored on each side. in the partially tapped counterbore on its left hand side, the side toward piston 124 of the adiabatic compression machine, this head receives diaphragm 26, hold down ring 128, and hold down nut 13o. Diaphragm llzd may be made of metal, for example aluminum. On its rim or ange portion, this vdiaphragm is clamped tightly between hold down ring '12d and an internal shoulder of cylinder head 114. In

its central portion, diaphragm 126 is convex toward piston 124, and this central portion may be initially scored so that it will rupture very rapidly under pressure exerted from combustion chamber space 132 once the diaphragm has been punctured by probe 68.

In the partially tapped counterbore on the right hand side of the cylinder head there is received a sealing gasket 134 and the threaded left hand end of expansion chamber tubular portion 62 of sampling device 60. Diaphragm puncturing probe 68 disposed essentially axially within this tubular portion is supported therein near its own left hand or pointed end by strut 136. This strut has a cylindrical middle portion with a central opening therein providing free Sliding passage for the probe, and beyond this middle portion is of streamlined cross section as indicated in FIG. 4. Such a cross section causes the strut to offer relatively little resistance to the flow of gaseous material from the combustion chamber into the expansion chamber.

The threaded right hand end of expansion chamber tubular portion 62 is screwed into the structure of expansion chamber enlarged portion 64 and sealed therein against gasket 138 which, along with gasket 134, may be of any suitable material. Expansion chamber enlarged portion 62 itself comprises a left hand and outside wall section 140, a right hand wail section 142 joined gastightly thereto as by welding or brazing, a left hand boss 144 joined gas-tightly to section 140, and a right hand boss 146 joined similarly to section 142. The left hand surface of right hand wall section 142 is designated 66 as noted in FIG. 1. Whatever other characteristics wall section 142 may have, this left hand surface of it should be convex toward the head end of the adiabatic compression machine. lt should be noted that right hand boss 146 protrudes through right hand wall section 142 into the enlarged expansion chamber space. It should be noted further that within this space the end of boss member 146 is beveled or chamfered at about a 45 angle. Such beveling is desirable to keep gases rushing into the expansion chamber enlarged portion from hitting against a locally rather at surface on wall section 142 directly opposite the right hand end of expansion chamber tubular portion 62.

Diaphragm puncturing probe 68 comprises a needle member 148 which extends all the way through expansion chamber tubular and enlarged portions 62 and 64. Its passage through right hand boss 146 of expansion charnber enlarged portion 64 is sealed by G-rings 150 and 152. After passing through boss 146, needle member 148 ex- 'tends part way along the bore of solenoid support piece 154. This support piece is threaded externally at its left hand end and internally at its right hand end. At its left hand end it is screwed into and shouldered against the right hand boss of expansion chamber enlarged portion 64. At its own right hand end, support piece 154 has spring sleeve 156 screwed into and shouldered against it.

The right hand end of needle member 148 of diaphragm puncturing probe 68 is screwed into coupling collar 158 and held in set engagement therewith by lock nut 161i. At its own right hand end, coupling collar 158 has cooking piece 162 secured ixedly to it. Indeed, coupling collar 158 and cooking piece 162 may be formed integrally. The threaded interior length of the coupling collar is suicient to allow at least some adjustment of needle member 148 within it while still retaining an adequate number of engaged threads between these two parts for strength purposes of their assembly. It is by means of this adjustment that the overall length of diaphragm puncturing probe is regulated. Specifically, it is by means of this adjustment that the distance is regulated between diaaphragm 126 and the pointed end of needle member 148 with probe 68 in cocked position.

Cocking piece 162 is provided with an external shoulder somewhat to the right of coupling collar 158, and this 8 shoulder is adapted to be engaged by plunger element 164 of electrical solenoid 62, which element passes downwardly through a radial hole in solenoid support piece 154. It is by means of the engagement of plunger element 164 with the shoulder of cocking piece 162 that diaphragm puncturing probe 68 is held in a cocked position, there .being no rlow of energizing current in the coil element of electrical solenoid 72. When there is a flow of current through this coil element, as there will be upon the closing of switch 188 by pendulum 18, plunger element 164 will be raised and the aforedescribed engagement discontinued.

To the right of its shoulder shown engaged with solenoid plunger element 164, diaphragm puncturing probe cocking piece 162 is provided with a spring-retaining collar 166. 'Ihis collar holds a coil spring 168 in compression etween itself and the interior end surface of spring sleeve 156. Cooking piece 162 extends substantially axially through spring 168 and also through a clear hole in the end wall portion of sleeve 156, in which hole it has a free sliding fit. At its extreme right hand end, cooking piece 162 has cooking knob 70 fastened to it to complete the assembly of diaphragm puncturing probe 68, and that of sampling device 68. In an actual embodiment of this Adevice associated with an adiabatic compression machine,

the following approximate dimensions obtained:

In. Cylinder bore of adiabatic compression machine 2 Clearance from piston to cylinder head at end of compression stroke '1/2 Length of expansion chamber tubular portion l() Length of expansion chamber enlarged portion 4 Diameterof expansion chamber tubular portion 1/2 Diameter of expansion chamber enlarged portion-" 61/2 Distance from pointed end of probe to diaphragm with probe in cocked position 975,6

The overall assembly of sampling device 60 may be tak-en as including, among other things, cylinder head 114 and the various parts screwed or otherwise fitted thereinto. It may also be taken as including collar 116 and clamping ring 118 as loose parts.

Referring next to FIGS. 5, 6, and 7 in general, what are shown are pressure-time records of events within the cylinder of an adiabatic compression machine, these events including the quenching of precombustion reactions of benzene/air mixtures at various times during the ignition delay periods of the mixtures under compression, and such quenching being effected by apparatuses and methods both according to the present invention and at variance from it. Specically FIGS. 5, 6, and 7 represent pressure-time traces as they appeared on developed photographic film previously exposed by a camera such as 54 in alignment with the viewing face of an oscilloscope receiving input voltages corresponding to signals generated at a pressure-to-voltage transducer or pressure pickup such as 44 set in the head of the adiabatic compression machine. In all cases the combustible mixture in the machine cylinder was a stoichiometric one. The benzene used was of reagent grade having a boiling range of 0.2 C. including the temperature 80.1 C.

Referring particularly now to FIG. 5, the pressure-time trace shown therein was obtained when a benzene/air mixture reacting at about 485 p.s.i.a. and about 1580" F. (860 C.) was expanded into an evacuated (4 mm. Hg abs.) cylindrical chamber of uniform cross section; that is, the expansion chamber into which the mixture in the combustion chamber was released after rupture of the separating diaphragm had only a long, slim tubular portion such as 62. Specifically, the expansion chamber did not have an enlarged portion such as 64 at the end of its tubular portion distant from the head of the adiabatic compression machine. Although, as FIG. 5 shows, a rapid, smooth initial quench or reduction in pressure was obtained with a chamber of uniform cross-section, this pressure reduction was not permanent; that is, there was subsequently an abrupt and somewhat irregular pressure r-ise to point A.

To determine the cause of the post-quenching pressure rise, runs were made -with the sampling device of uniform cross-section expansion chamber at various ratios of pressure across the separating diaphragm just prior to rupture. The time from diaphragm rupture for a high pressure reflected shock wave and the low pressure boundary or contact surface of the smoothly expanding gaseous materials to interact was calculated from shock tube relations for each pressure ratio. These calculated time values were then compared with times from diaphragm rupture to the -abrupt pressure rise measured from the photographic records. Close correspondence of calculated and measured times was found in each case, and this suggested that the pressure rise after quench was generated by a reflected shock wave. This conclusion was established further when runs were made with the expansion chamber packed with glass wool which attenuated the shock wave. Pressure-time records for these runs showed that presure remained constant after the quench. The absolute value of pressure rise to point A, however, was considerably greater than that which could have been due to only the pressure of the reflected shock wave itself, thus in-dicating that the wave had acted as an initiator of further reactions.

Referring next to FIG. 6, the pressure-:time trace shown therein was obtained when a benzene/ air mixture reacting at about 497 p.s.i.a. and about 258() F. (1415 C.) was expanded int-o a sampling device generally similar to that shown in FIGS. l and 2. Specifically, the expansion chamber of this device had -a long, slim tubular portion such as 62 and an enlarged portion such Las 64, this enlarged portion being characterized by an interior surface such as 66 convex toward the adiabatic compression machine. Prior to rupture of the separating diaphragm, the expansion chamber was filled with helium gas at a pressure of about 30.0 p.s.i.a. (15.3 p.s.i.g.) and 72 F- (22 C.) In the isentropic expansion or quenching process started at a point three quarters 4through the ignition -delay period, the reacting mixture was quenched in about 0.9 millisecond from the aforesaid pressure and temperature to .about lli-i2 p.s.i.a. and about lli-70 F. (799 C), as calculated from shock tube equations for the steady-state, one dimensional case.

Following the isentropic expansion, the gases cooled further to room temperature and had a final partial pressure of about 28 p.s.i.a. Gas chromatographic analysis of the quenched reaction products showed that 85-90% of the benzene had undergone reaction. What is to be noted particularly in FIG. 6 is the absence of any irregular pressure rise (such as that to point A in FIG. following the smooth, initial decrease in pressure or isentropic expansion consequent upon diaphragm rupture. It is felt that this shows clearly the effectiveness of the expansion chamber enlarged portion 64 and its specially shaped interior -wall surface 66 to prevent shock wave reflection which would cause further precombustion reaction and an attendant increase in pressure.

Referring nally to FIG. 7, the pressure-time trace shown -therein was obtained when a benzene/ air mixture was quenched by means of the apparatus and according to the lmethod of this invention from a pressure of about 272 p.s.i.a. and a temperature of abou-t 735 F. (390 C.), diaphragm rupture and hence the start of quenching taking place j-ust at the end of a compressing stroke of the adiabatic compression machine. The compressed mixture Was isentropically expanded or quenched to about 45 p.s.i.a. and 330 F. (165 C.) in about 0.8 millisecond, la pressure of 5.9 p.s.i.a. due to helium gas having existed within the expansion chamber prior to diaphragm rupture. Following the isentropic expansion, the gases cooled further to room temperature and had a final partial pressure of about 7 p.s.i.a. The quenched 1;() mixture was transferred to and condensed in a stainless steel sample coil such as 85.

Gas chromatographic analysis of this mixture showed that no significant oxidation of the benzene had occurred during the compression stroke. in this connection, it is important to note that in delay time measurements it has always been assumed (without supporting data) that the fuel/air mixture does not undergo extensive reactions during compression. The aforementioned analysis establishes, at least for the benzene/ air mixture, that reactions during compression are negligible, and that the end of compression is a valid point from which to measure ignition delays.

Although this invention .has been describedwith a certain degree of particularity, it is to be understood that the present disclosure has been made only by way of example, especially with respect to numerical values and particular reacting materials to be sampled given herein, and that numerous changes in the details of machine elements and assemblies and of choice of chemical reactions `operated upon thereby may be resorted to without departing from the spirit and scope of this invention as set forth in the following claims which are to be construed as -broadly as the state of the relevant art allows.

What is claimed is:

1.An apparatus for sampling intermediate products of chemical reactions, s-aid appara-tus comprising (l) a first expansion chamber portion having a length at least several times greater' than its bore and having further a tirs-t end and a second end, (2) a diaphragm closing said first expansion chamber portion Iat the rst end thereof, (3) a second expansion chamber portion extending `beyond said first expansion chamber portion and having an inside diameter appreci-ably greater than the bore of said first expansion chamber portion, (4) a first wall portion disposed substantially .transversely to said second expansion chamber portion at the first end thereof, said first wall portion being joined to said rst expansion cramber portion at the second end thereof and said first wall portion closing said second expansion chamber portion at the first end thereof except where open to the interior of said first expansion chamber portion to place said iirst and second chamber portions in communication, (5) a second wall portion substantially closing said second expansion chamber portion at the second end thereof, (6) a diaphragm puncturing probe mov-ably disposed within at least said first expansion chamber p0rtion substantially parallel to the axis thereof, (7) positive driving means engaged with said probe tending t-o move the same toward, against, and through said diaphragm, (8) retaining means engageable with said probe whereby the same may be held out of contact with said diaphragm against the force of said driving means, (9) releasing means cooperable with said retaining means whereby the same may be disengaged from sai-d probe, and (l0) means connecting the second end of said first expansion chamber with the environment being sampled so that said reaction products can pass into said first expansion chamber when vsaid diaphragm is punctured.

`2. An apparatus according to claim l in which said diaphragm is concave toward the second end of said first expansion chamber portion.

3. An apparatus according to claim 1 in which said second expansion chamber portion is -appreciably shorter than said rst expansion chamber portion.

4. An apparatus according to claim l in which the surface of said second wall portion forming -an interior surface of said second expansion chamber portion is convex toward said diaphragm in order to aid in dissipating any shock 'wave reflected from said surface.

5. An apparatus according to claim l which further comprises valved conduit means communicating with the region within said expansion chamber portions where- 11 through gaseous ymaterial may be charged into and removed from said region.

6. An apparatus according -to claim l wherein said positive driving means comprise spring loaded driving means.

7. A method of sampling intermediate products of chemical reactions, said method comprising the steps of (l) placing a reaction region containing still-reacting products in communication with `an expansion region, said placing step being effected abruptly at a predetermined point in time and the initial total pressure within said reaction region being greater than that within said eX- pansion region, (2) expanding said products into said expansion region to develop a pressure shock wave traveling away from said reac-tion region `and a rarefaction wave traveling toward and through said reaction region whereby said products are essentially isentropically cooled and the continuing reaction thereof terminated ato leave said products in the ycondition of quenched intermediates, and (3) withdrawing said intermediate products from said communicating reaction and expansion regions.

References Cited in the le of this patent Metcalf Apr. 24, l945 

1. AN APPARATUS FOR SAMPLING INTERMEDIATE PRODUCTS OF CHEMICAL REACTIONS, SAID APPARATUS COMPRISING (1) A FIRST EXPANSION CHAMBER PORTION HAVING A LENGTH AT LEAST SEVERAL TIMES GREATER THAN ITS BORE AND HAVING FURTHER A FIRST END AND A SECOND END, (2) A DIAPHRAGM CLOSING SAID FIRST EXPANSION CHAMBER PORTION AT THE FIRST END THEREOF, (3) A SECOND EXPANSION CHAMBER PORTION EXTENDING BEYOND SAID FIRST EXPANSION CHAMBER PORTION AND HAVING AN INSIDE DIAMETER APPRECIABLY GREATER THAN THE BORE OF SAID FIRST EXPANSION CHAMBER PORTION, (4) A FIRST WALL PORTION DISPOSED SUBSTANTIALLY TRANSVERSELY TO SAID SECOND EXPANSION CHAMBER PORTION AT THE FIRST END THEREOF, SAID FIRST WALL PORTION BEING JOINED TO SAID FIRST EXPANSION CHAMBER PORTION AT THE SECOND END THEREOF AND SAID FIRST WALL PORTION CLOSING SAID SECOND EXPANSION CHAMBER PORTION AT THE FIRST END THEREOF EXCEPT WHERE OPEN TO THE INTERIOR OF SAID FIRST EXPANSION CHAMBER PORTION TO PLACE SAID FIRST AND SECOND CHAMBER PORTIONS IN COMMUNICATION, (5) A SECOND WALL PORTION SUBSTANTIALLY CLOSING 